Process of treating waste containing zinc oxide

ABSTRACT

A treating method of recovering zinc in the metal state from a waste containing the zinc in the oxide state, lead, chlorine, fluorine, and water comprising a mixing process 90 of obtaining a to-be-treated mixed material 70 by mixing a steel dust 7 and a reducing material 8 together; a chlorine recovery process 91 of recovering the chlorine and the water by heating the to-be-treated mixed material 70; a lead recovery process 92 of recovering fluorine and lead by heating the to-be-treated mixed material 70 under vacuum; a zinc recovery process 93 of recovering metallic zinc by heating the to-be-treated mixed material 70 at a temperature higher than that in the lead recovery process 92 with the vacuum state maintained so as to reduce and vaporize zinc; and a residue recovery process 94 of recovering a residue 79 of the to-be-treated mixed material 70. This construction allows the metallic zinc to be recovered at a high purity from a zinc oxide-containing waste and an on-site treatment to be accomplished.

TECHNICAL FIELD

The present invention relates to a waste-treating method of recoveringzinc in the metal state from wastes containing zinc in the oxide state.

BACKGROUND ART

Among various wastes generated by industrial production, thosecontaining harmful substances such as zinc, lead, and the like areparticularly required to be treated safely.

As the zinc-containing waste, there are one such as pressed scraps ofgalvanized sheets containing the zinc in the metal state and the othersuch as steel dust containing the zinc in the oxide state.

In the case of the zinc-containing waste in the metal state, asdisclosed in Japanese Laid-Open Patent Publication No. 4-346681, it ispossible to recover the zinc from the waste by heating the waste undervacuum to vaporize the zinc from steel. Thus, metal zinc can berecovered comparatively easily.

In the case of the zinc oxide-containing waste which contains the zincin the oxide state, it is difficult to recover the metal zinc by theabove-described method.

Thus, in treating the waste containing the zinc oxide, the followingmethod is known: The waste is heated to a temperature of 1,200° C. orhigher by means of a burner in a rotary kiln method so that the ZnO(zinc oxide) makes a reducing reaction with coke, coal, or the like.

However, since this method necessitates the waste to be heated to a veryhigh temperature, it leads to a highly increased energy cost. Further,the method has another problem that the metal zinc obtained by reducingthe zinc oxide is oxidized again when it is recovered and thus it isdifficult to recover zinc in the metal state. Furthermore, the method isuneconomical unless the waste is treated in a large amount.

As another method, the zinc is vaporized by plasma at a high temperatureto recover the zinc in the metal state by means of a lead splashcondenser. However, it is difficult for this method to perform so-calledon-site treatment that is capable of treating the whole amount of thegenerated waste at the site, such as a plant, where the waste has beengenerated, because this method exerts bad influence unavoidably onenvironment in treating the waste. Thus, it is necessary to transfer thewaste to a specific waste-treating site having anenvironment-nonpolluting equipment.

Under these circumstances, the zinc is recovered in the zinc oxide statefrom a part of the waste containing the zinc oxide by a rotary kilnmethod and then the recovered zinc oxide is refined to recycle it,whereas the remaining part of the waste is transferred to the specificwaste-treating site to have it reclaimed there, in consideration of thelegal regulation.

However, it is difficult to continue to perform the above-mentionedcontrolled discard of the waste in the future due to problems such as ashortage of the waste-treating sites and a high processing cost.

Moreover, it is not economically preferable to discard materials such asthe zinc contained in the waste without recycling them.

Under these circumstances, needs exist for the development of artscapable of recovering the zinc with other harmful substances from thewaste containing the zinc oxide and recovering the zinc in the metalstate at a high purity to recycle it.

Mr. Azakami et al. of Tohoku University proposed a two-stagevacuum-reducing method for recovering the metallic zinc from zincoxide-containing waste (quoted from magazines of Japan Mining IndustrySociety, No. 1203 of volume 104, No. 1206 of volume 104 and No. 1209 ofvolume 104.) However, since CO gas is used to reduce iron oxidecontained in the waste in the first stage of the two-stagevacuum-reducing method, and then the zinc is reduced by using thereduced iron obtained in the second stage, a reducing reaction thatlasts for more than three hours is required. Thus, this method is noteconomical and difficult to industrialize accomplishment of the on-sitetreatment.

In view of the above-described conventional problems, it is accordinglyan object of the present invention to provide a zinc oxide-containingwaste-treating method capable of recovering metallic zinc therefrom at ahigh purity in a short time period and accomplishing the on-sitetreatment.

DISCLOSURE OF THE INVENTION

The invention, according to claim 1, discloses a treating method ofrecovering zinc in the metal state from a waste containing the zinc inthe oxide state, lead, chlorine, fluorine, and water, comprising:

a mixing process of mixing the waste and a reducing material together toobtain a to-be-treated mixed material;

a chlorine recovery process of recovering the chlorine and the water byheating the to-be-treated mixed material;

a lead recovery process of recovering the fluorine and the lead byheating the to-be-treated mixed material under a vacuum state;

a zinc recovery process of reducing and vaporizing the zinc to recovermetallic zinc by heating the to-be-treated mixed material at atemperature higher than that set in the lead recovery process, with thevacuum state maintained; and

a residue recovery process of recovering a residue of the to-be-treatedmixed material.

The most remarkable feature of this invention is that initially, theto-be-treated mixed material is prepared, and then, after the chlorinerecovery process finishes, the lead recovery process and the zincrecovery process are performed under vacuum, and the heating temperaturein the zinc recovery process is higher than that set in the leadrecovery process.

The mixing process and the chlorine recovery process are not required tobe carried out under vacuum but they are performed in an atmosphericenvironment.

It is necessary to carry out the lead recovery process and the zincrecovery process under vacuum and maintain the vacuum state when theexecution of the lead recovery process is transferred to that of thezinc recovery process.

The residue recovery process may be carried out in the atmosphericenvironment, but as will be described later, when the residue iscompression-molded into a briquette, preferably, the residue recoveryprocess is performed in the vacuum state.

The heating oven may be changed for each process but one heating ovenmay be used for a plurality of processes. When one heating oven is usedfor a plurality of processes, a method of sequentially changing theheating condition can be adopted.

In the lead recovery process and the zinc recovery process and at thetime of the transfer from the execution of the lead recovery process tothat of the zinc recovery process, the heating oven having a function ofmaintaining the vacuum state is used.

The heating oven is required to be provided with a recovery containerfor recovering substances which have separated by means of vaporizationor the like from the to-be-treated mixed material. In particular, ametallic zinc recovery container is provided with the heating oven whichis used in the zinc recovery process.

As the reducing material, various industrial wastes, car dust, and thelike containing carbon are used, as will be described later.

Preferably, the mixing ratio of the reducing material to the waste is30-100 wt %. If the mixing amount of the reducing material is less than30 wt %, the reducing reaction of zinc oxide does not occursufficiently, whereas if the mixing amount of the reducing material ismore than 100 wt %, the proportion of the reducing material whichremains in the residue becomes too high.

The operation of the present invention will be described hereinafter.

In the present invention, initially, the waste and the reducing materialare mixed together in the mixing process and then, the mixture is putinto the heating oven for carrying out the chlorine recovery process.

Then, in the chlorine recovery process, the to-be-treated mixed materialis heated to a temperature at which chlorine and water can be recovered.As a result, the chlorine and the water are separated from theto-be-treated mixed material and recovered.

Then, in the lead recovery process, after the inside of the heating ovenprovided with the to-be-treated mixed material is set to be undervacuum, the to-be-treated mixed material is heated to a temperaturewhich is lower than the temperature at which the zinc oxide is reducedand lead and fluorine can be recovered. Consequently, the lead in anoxide state is reduced and vaporizes or volatilizes in the oxide stateand recovered.

Then, in the zinc recovery process, the to-be-treated mixed material isheated at a temperature higher than that set in the lead recoveryprocess, with the vacuum state maintained. That is, the to-be-treatedmixed material is heated at a temperature higher than the temperature atwhich the zinc oxide is reduced. As a result, the zinc oxide is reducedby the reducing material and becomes metallic, thus vaporizing.Therefore, the zinc can be recovered in the metal state by the metalliczinc recovery container.

Then, the residue is recovered in the residue recovery process, and apart thereof can be recycled as a raw material of steel.

Further, in the present invention, because harmful substances can besequentially recovered, as described above, no bad influence is exertedon the environment, and the treating time required to carry out eachprocess is comparatively short.

Accordingly, an on-site treatment can be accomplished easily.

As defined in claim 2, it is preferable that the to-be-treated mixedmaterial is heated at 40-600° C. in the chlorine recovery process. Ifthe heating temperature is lower than 40° C., the chlorine cannot berecovered sufficiently. It is preferable that the heating temperature ishigher than 200° C. If the heating temperature is higher than 600° C.,even the zinc which should be recovered in one of the subsequentprocesses is recovered in the chlorine recovery process.

As defined in claim 3, preferably, the to-be-treated mixed material isheated at 200-600° C. in the lead recovery process. If the heatingtemperature is lower than 200° C., it is difficult to recover the lead.If the heating temperature is higher than 600° C., the zinc which shouldbe recovered in the next process may be reduced by the reducing materialand recovered in the lead recovery process.

As a method of providing a mixing process of mixing the reducingmaterial with the to-be-treated mixed material after the chlorinerecovery process and the lead recovery process finish without adding thereducing material to the to-be-treated mixed material and thenperforming the zinc recovery process and the residue recovery process,the following method is carried out.

That is, as defined in claim 4, there is provided a treating method ofrecovering zinc in the metal state from a waste containing zinc in theoxide state, lead, chlorine, fluorine, and water, comprising:

a chlorine recovery process of recovering the chlorine and the water byheating the waste;

a lead recovery process of recovering the fluorine and the lead byheating the waste in a vacuum state;

a mixing process of mixing a reducing material with the waste with thevacuum state maintained to obtain a to-be-treated mixed material;

a zinc recovery process of reducing and vaporizing the zinc to obtainmetallic zinc by heating the to-be-treated mixed material, with thevacuum state maintained; and

a residue recovery process of recovering a residue of the to-be-treatedmixed material.

The characteristic of the invention of claim 4 is that as describedabove, the reducing material is not mixed with the waste until the zincrecovery process is carried out.

In this manner, the progress of the reducing reaction of the zinc oxidecan be restrained to a possible highest degree in the processes prior tothe zinc recovery process. Thus, the reducing and vaporization reactionsof the zinc can be allowed to occur mainly in the zinc recovery processand hence, the recovery percentage of metallic zinc can be increased.

In the case of the method of mixing the reducing material with the wastein the first process, the zinc oxide will be reduced in a small amountand vaporize in the presence of the reducing material in the leadrecovery process. Thus, there is a disadvantage that the amount of themetallic zinc which can be recovered in the subsequent zinc recoveryprocess is reduced a little. The invention of claim 4 can get over thisdisadvantage.

In the lead recovery process, the lead can be recovered without thepresence of the reducing material. This is because most of the leadcontained in the waste volatilizes in the oxide state. Because the leadrecovery process is performed under vacuum as described above, thevolatile reaction can be easily accomplished at a temperature lower thanthat in the atmospheric pressure.

The invention of claim 4 is similar to that of the invention of claim 1in other operations.

It is preferable to set the heating temperature as described below ineach process in the invention of claim 4.

That is, as defined in claim 5, it is preferable that the waste isheated at 40-900° C. in the chlorine recovery process. If the waste isheated at a temperature lower than 40° C., it is difficult to recoverchlorine sufficiently. It is preferable that the waste is heated at aheating temperature higher than 200° C. If the waste is heated at atemperature higher than 900° C., the zinc which should be recovered inone of the subsequent processes may be recovered in this process. It ispreferable that the heating temperature is set to be lower than 750° C.It is preferable that as defined in claim 6, the waste is heated at200-900° C. in the lead recovery process. If the heating temperature islower than 200° C., there is a problem that it is difficult to recoverthe lead. If the heating temperature is even higher than 900° C., theeffect of improving the recovery efficiency of the lead is still low.Thus, there is no effect in heating the waste at a temperature higherthan 900° C.

The reason for that the upper limit temperature in the chlorine recoveryprocess of the invention of claim 5 is set to be higher than that in thechlorine recovery process of the invention of claim 2 and the reason forthat the upper limit temperature in the lead recovery process of theinvention of claim 6 is set to be higher than that in the lead recoveryprocess of the invention of claim 3 are because treatments in theinventions of claims 5 and 6 are carried out without mixing the reducingmaterial with the waste, unlike the invention of claims 2 and 3.

In any one of the inventions of claims 1 through 6, the to-be-treatedmixed material is preferably heated at 600-1,100° C. in the zincrecovery process, as defined in claim 7. If the heating temperature islower than 600° C., the reducing reaction of the zinc does not occursufficiently, whereas if the heating temperature is higher than 1,100°C., the energy cost required to heat the to-be-treated mixed materialincreases.

The present invention provides another method as follows:

As defined in claim 8, there is provided a treating method of recoveringzinc in the metal state from a waste containing the zinc in the oxidestate, lead, chlorine, fluorine, and water, comprising:

a mixing process of mixing the waste and a reducing material together toobtain a to-be-treated mixed material;

a chlorine and lead recovery process of recovering the lead, thechlorine, the fluorine, and the water by heating the to-be-treated mixedmaterial;

a zinc recovery process of reducing and vaporizing the zinc to obtainmetallic zinc by heating the to-be-treated mixed material in a vacuumstate; and

a residue recovery process of recovering a residue of the to-be-treatedmixed material.

The most remarkable feature in the invention of claim 8 is that afterthe lead, the chlorine, fluorine, and water are recovered in one process(chlorine and lead recovery process), the zinc recovery process iscarried out under vacuum.

According to this method, the metallic zinc can be recovered at a highpurity by only two-time heating and further, the treatment period oftime can be reduced. Thus, the method allows the on-site treatment to beaccomplished more easily.

In the invention of claim 8, the chlorine and lead recovery process isperformed in the atmospheric environment. That is, the fluorine and thelead can be recovered without producing a vacuum. This is because thereducing material makes a volatile action while it is making a reducingreaction.

The action which occurs in the zinc recovery process and that whichoccurs in the residue recovery process are similar to that of theinvention of claim 1.

As defined in claim 9, it is preferable that the to-be-treated mixedmaterial is heated at 40-750° C. in the chlorine and lead recoveryprocess. If the heating temperature is lower than 40° C., it isdifficult to recover the chlorine and the lead sufficiently, andpreferably the heating temperature is set to be 200° C. or higher. Ifthe heating temperature is higher than 750° C., the zinc which should berecovered in the next process may be recovered in this process due tothe action of the reducing material. The reason for that the upper limittemperature in the invention of claim 9 is set to be higher than thatset in the invention of claims 2 and 3 is because this process iscarried out without producing a vacuum, unlike the invention of claims 2and 3.

As defined in claim 10, it is preferable that the to-be-treated mixedmaterial is heated at 600-1,100° C. in the zinc recovery process. If theheating temperature is lower than 600° C., the reducing reaction doesnot occur sufficiently. If the heating temperature is higher than 1,100°C., the energy cost is increased and a high heating performance isrequired, resulting in the higher cost of the equipment.

As defined in claim 11, in all the above-described methods, it ispreferable that the residue is recovered by compression-molding theresidue into a briquette, with the vacuum state maintained in theresidue recovery process. In this manner, the residue can becompression-molded into the briquette without being oxidized. Therefore,the obtained briquette has a certain degree of strength because iron inthe residue is sintered.

Therefore, the residue can be easily handled as the briquette. Forexample, it can be easily recycled as a raw material of steel.

As defined in claim 12, one or more industrial wastes selected fromiron-containing industrial wastes which contains Fe and/or FeO andcarbon-containing industrial wastes which contains carbon can be used asthe reducing material. The invention of claim 12 eliminates the need forproducing a particular reducing material, thus making it possible toutilize wastes in conformity to the object of the present invention.

The iron-containing industrial waste includes shot dust, hot scarferdust, abrasive dust, and the like. The carbon-containing waste includeswood waste, sawdust, tire dust, and the like.

As defined in claim 13, car dust comprising organic substances recoveredfrom materials of a discarded automotive body can be used as thereducing material. The invention of claim 13 allows the car dust to beeffectively utilized without disposing at a very high cost.

As defined in claim 14, it is preferable that the degree of vacuum inthe vacuum state in each of the processes is 0.001-20 Torr. The reasonfor that the preferable lower limit vacuum degree is set to 0.001 Torris because the cost of the equipment is high to achieve a vacuum degreelower than 0.001 Torr and in addition, the reaction efficiency cannot beimproved much is low even though a vacuum degree lower than 0.001 Torris set as the lower limit vacuum degree in carrying out the treatments.The reason for that the preferable upper limit vacuum degree is set to20 Torr is because at a vacuum degree higher than 20 Torr, a sufficientrecovery percentage cannot be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing the process of a treating methodaccording to Embodiment 1.

FIG. 2 is an explanatory view showing the construction of a treatingequipment according to Embodiment 1.

FIG. 3 is an explanatory view showing the relationship between the gramequivalent of a reducing material and a zinc recovery percentageaccording to Embodiment 2.

FIG. 4 is an explanatory view showing the process of a treating methodaccording to Embodiment 3.

FIG. 5 is an explanatory view showing the process of a treating methodaccording to Embodiment 4.

FIG. 6 is an explanatory view showing the construction of a treatingequipment according to Embodiment 4.

FIG. 7 is an explanatory view showing the process of a treating methodaccording to Embodiment 5.

DESCRIPTION OF REFERENCE NUMERALS

1, 102: treating equipment

10: feeding portion

11: first heating oven

12: second heating oven

13: third heating oven

14: briquette machine

21-24: vacuum pump

31-34: material passageway

301-304: valve

41-44: first -fourth recovery container

52, 53: metal recovery container

7: steel dust

8: reducing material

90: mixing process

91: chlorine recovery process

910: chlorine and lead recovery process

92: lead recovery process

93: zinc recovery process

94: residue recovery process

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1

With reference to FIGS. 1 and 2 and tables 1 through 4, the method oftreating a zinc oxide-containing waste according to Embodiment 1 of thepresent invention will be described hereinafter.

As the method of Embodiment 1, the method of treating steel dust whichis generated when steel is manufactured is described hereinafter.

As shown in table 1, the steel dust contains zinc in the oxide state,and contains lead, chlorine, fluorine, and water.

As shown in FIGS. 1 and 2, the steel dust is treated by a methodcomprising a mixing process 90 of obtaining a to-be-treated mixedmaterial 70 by mixing a steel dust 7 and a reducing material 8 together;a chlorine recovery process 91 of recovering the chlorine and the waterby heating the to-be-treated mixed material 70; a lead recovery process92 of recovering fluorine and lead by heating the to-be-treated mixedmaterial 70 under vacuum; a zinc recovery process 93 of recoveringmetallic zinc by heating the to-be-treated mixed material 70 at atemperature higher than that in the lead recovery process 92 so as toreduce and vaporize zinc, with the vacuum state maintained; and aresidue recovery process 94 of recovering a residue 79 of theto-be-treated mixed material 70.

The method will be described in detail hereinafter.

Initially, as shown in FIG. 2, as the equipment for carrying out themethod, an equipment 1 comprising a feeding portion 10, a first heatingoven 11, a second heating oven 12, a third heating oven 13, and abriquette machine 14 is used.

The first heating oven 11, the second heating oven 12, the third heatingoven 13, and the briquette machine 14 are connected with vacuum pumps21-24, respectively. The atmosphere inside the second and third heatingovens 12 and 13 and the briquette machine 14 can be made vacuum by meansof the vacuum pumps 22, 23, and 24, respectively.

As shown in FIG. 2, first through fourth recovery containers 41-44 areprovided at the exhaust side of each of the vacuum pumps 21-24. Metalrecovery containers 52 and 53 are interposed between the second heatingoven 12 and the vacuum pump 22 and between the third heating oven 13 andthe vacuum pump 23, respectively.

The first and second recovery containers 41 and 42 are charged withabsorbent such as chlorine and fluorine and have a dust-recoveringfunction, and the third and fourth recovery containers 43 and 44 have adust-recovering function.

The metal recovery containers 52 and 53 recover metal by condensingvaporized metal and are constituted so as to be kept at a temperaturelower than the condensation temperature of metal to be recovered.

As shown in FIG. 2, material passageways 31-34 for feeding theto-be-treated mixed material 70 are provided at the upstream anddownstream sides of the respective heating ovens, and valves 301-304 areinstalled on the material passageways 31-34, respectively.

In treating the steel dust 7 by using the treating equipment 1, hotscarfer dust (FeO=99.5%) which is iron-containing industrial waste isprepared as the reducing material 8, and the hot scarfer and the steeldust 7 are mixed together at a ratio of 1:1.

As shown in FIG. 2, initially, the steel dust 7 and the reducingmaterial 8 are fed to the feeding portion 10 to mix them together.

Then, the to-be-treated mixed material 70 obtained by the mixing process90 is fed to the first heating oven 11 by opening the valve 301 of thematerial passageway 31 of the treating equipment 1. Then, after thevalve 301 is closed, the to-be-treated mixed material 70 is heated atabout 200° C. for one hour and the vacuum pump 21 is actuated to exhaustthe atmosphere inside the first heating oven 11 to the first recoverycontainer 41. Consequently, the chlorine and the water separate from theto-be-treated mixed material 70 and are recovered by the first recoverycontainer 41.

Then, after the chlorine recovery process 91 finishes, the to-be-treatedmixed material 70 is fed to the second heating oven 12 by opening thevalve 302 of the material passageway 32. Then, after the valve 302 isclosed, the vacuum pump 22 is actuated to produce a vacuum at a degreeof 0.5 Torr inside the second heating oven 12.

Then, the to-be-treated mixed material 70 is heated at about 600° C. forone hour. As a result, the lead in the to-be-treated mixed material 70is reduced to metallic lead by the action of the reducing material 8 andvaporizes. Then, the metallic lead is condensed and recovered by themetal recovery container 52 kept at 200° C. lower than the condensationtemperature of the metallic lead. The fluorine separated from theto-be-treated mixed material 70 is recovered by the second recoverycontainer 42 positioned at the exhaust side of the vacuum pump 22.

After the lead recovery process 92 finishes, the to-be-treated mixedmaterial 70 is fed to the third heating oven 13 by opening the valve 303of the material passageway 33 of the treating equipment 1. At this time,a vacuum is produced at a degree of 0.5 Torr inside the third heatingoven 13 by actuating the vacuum pump 23. In this manner, the leadrecovery process 92 can be switched to the zinc recovery process 93,with the vacuum state maintained.

Then, after the valve 303 is closed, the to-be-treated mixed material 70is heated at about 900° C. for two hours. As a result, zinc oxide isreduced to metallic zinc and vaporizes. Then, the metallic zinc whichhas vaporized is condensed and recovered by the metal recovery container53 kept at 400° C. lower than the condensation temperature thereof.Other substances separated from the to-be-treated mixed material 70 arerecovered by the third recovery container 43 positioned at the exhaustside of the vacuum pump 23.

Then, after the zinc recovery process 93 finishes, the residue 79 is fedto the briquette machine 14 by opening the valve 304 of the materialpassageway 34. At this time, too, the atmosphere inside the briquettemachine 14 is made vacuum at a vacuum degree of 0.5 Torr by actuatingthe vacuum pump 24. In this manner, the zinc recovery process 93 can beswitched to the residue recovery process 94, with the vacuum statemaintained.

Then, the residue 79 is compression-molded into a briquette 795 by acompressor 141 of the briquette machine 14. In this manner, a series ofthe treatments are accomplished.

The briquette 795 thus obtained is recycled as a raw material of steel.

Tables 2, 3 and 4 show the results obtained by sampling and analyzingthe components of the to-be-treated mixed material 70 obtained after therespective processes finish and the components of the material obtainedfrom the metal recovery container 53.

Table 2 shows the values of the representative components of theto-be-treated mixed material 70 obtained immediately after the leadrecovery process 92 finishes. AS indicated in table 2, the lead (Pb) andthe fluorine (F) contained in the steel dust 7 at the initial stageshown in table 1 have been recovered sufficiently.

Table 3 shows the values of the representative components of theto-be-treated mixed material 70 obtained immediately after the zincrecovery process 93 finishes, namely, the representative components ofthe residue 79. As indicated in table 3, the zinc (zn) contained in thesteel dust 7 at the initial stage shown in table 1 has been recoveredsufficiently.

Table 4 shows the values of the components of the material obtained fromthe metal recovery container 53 in the zinc recovery process 93. Asindicated in table 4, the recovered material contains the metallic zincat a high purity of 89.2%.

Accordingly, in Embodiment 1, the recovered metallic zinc can berecycled without refining.

Further, as described above, in Embodiment 1, harmful substances such aslead can be recovered sequentially and the treatment period of time iscomparatively short. Thus, the method of the present invention issuitable for on-site treatment.

                  TABLE 1                                                         ______________________________________                                        Value of components contained in steel dust (Embodiments 1-6)                 Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             25.0   22.26  2.78 2.53 4.05 0.47 4.61 0.51 Bal-                        at %                                              ance                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Value of components contained in to-be-treated mixed material after lead      recovery process (Embodiment 1)                                               Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             34.6   19.7   3.38 0.20 5.43 0.64 0.22 0.01 Bal-                        at %                                              ance                        ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Value of components contained in residue (Embodiment 1)                       Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             72.50  0.01   3.80 0.20 5.60 0.68 0.23 0.01 Bal-                        at %                                              ance                        ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Value of recovered metallic zinc (Embodiment 1)                               Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             0.72   89.2   0.04 0.02 0.01 0.01 0.20 0.01 Bal-                        at %                                              ance                        ______________________________________                                    

Embodiment 2

In Embodiment 2, the correlation between the mixing amount of thereducing material 8 and the recovery percentage of the obtained metalliczinc was examined.

In the examination, the amount of the reducing material 8 necessary forreducing one mol of Zn (zinc) is set to one gram equivalent, and severalgram equivalent ratios were used in a range of about 2.4-24 so as toprepare the to-be-treated mixed material 70. The to-be-treated mixedmaterial 70 was treated in the procedure of Embodiment 1. As therecovery percentage of the obtained metallic zinc, the removalpercentage determined by dividing the percentage (at %) of the zinccontained in the residue by the percentage (at %) of the zinc containedin the to-be-treated mixed material was used.

In Embodiment 2, the heating temperature was set to 900° C. and 750° C.in the zinc recovery process to examine the influence caused by each ofthe temperatures.

FIG. 3 shows the result. The gram equivalent ratio of the reducingmaterial is shown on the abscissa and the recovery percentage (removalpercentage) of the zinc is shown on the ordinate. The distribution stateat the time when the heating temperature was 900° C. in the zincrecovery process is indicated by a dotted line E1 and that at the timewhen the heating temperature was 750° C. in the zinc recovery process isindicated by a solid line E2.

As indicated in FIG. 3, when the heating temperature in the zincrecovery process was 900° C., a high zinc recovery percentage wasobtained in the entire measured region, irrespective of gram equivalentratios. When the heating temperature in the zinc recovery process was750° C., the zinc recovery percentage was high in the case where thegram equivalent ratio was high, whereas the zinc recovery percentagedecreased as the gram equivalent ratio was lowered.

As will be understood from the foregoing description, when the heatingtemperature in the zinc recovery process was set to be higher than 900°C., high zinc recovery percentages can be always obtained by mixing thereducing material with the steel dust 7 such that the gram equivalentratio is 2.4 or more.

Embodiment 3

In Embodiment 3, as shown in FIG. 4, car dust 82 was used as thereducing material, unlike Embodiment 1. In the residue recovery process94, the residue was not molded into the briquette. Embodiment 3 issimilar to Embodiment 1 in other points.

The car dust 82 contains an organic material of a discarded automotivebody from which metallic materials were excluded, thus consisting of thecomponents shown in table 5. As indicated in table 5, the car dust 82contains harmful substances such as lead (Pb) in addition to carbon (C)which constitutes the main component of the reducing material. Thus,needs existed for the development of an effective treating method. Themethod of Embodiment 3 is capable of treating the car dust itself aswell as the steel dust by using the car dust having such a problem asthe reducing material.

Namely, in Embodiment 3, the lead can be recovered by heating theto-be-treated mixed material under vacuum in the lead recovery processwhich is carried out by the second heating oven 12, similarly toEmbodiment 1.

In the chlorine recovery process and the zinc recovery process, anoperation similar to that of Embodiment 1 is obtained, and consequentlythe residue consisting of the components shown in table 6 is obtained.

As indicated in table 6, the residue is obtained in the state in whichthe harmful substances have been satisfactory removed from the car dust.

Metallic zinc obtained in the zinc recovery process of Embodiment 3 hada high purity, similarly to that obtained in Embodiment 1.

                  TABLE 5                                                         ______________________________________                                        Value of components contained in car dust (Embodiment 3)                      Component                                                                             C      Fe    Cu  Pb  Al    Cl   F    Zn   H                           ______________________________________                                        Content at %                                                                          69.6   5.0   2.0 2.0 3.50  <0.01                                                                              <0.01                                                                              0.51 17.4                        ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Value of components contained in residue (Embodiment 3)                       Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             36.0   0.01   3.50 0.20 5.44 0.80 0.21 0.05 Bal-                        at %                                              ance                        ______________________________________                                    

Embodiment 4

In this embodiment, as shown in FIG. 5, the chlorine recovery process 91and the lead recovery process 92 are carried out before the reducingmaterial 8 is added to the steel dust 7, and then, the mixing process 90of mixing the reducing material 8 with the steel dust 7 is performed,and then, the zinc recovery process 93 and the residue recovery process94 are performed.

The steel dust 7 and the reducing material 8 of this embodiment aresimilar to those of Embodiment 1.

That is, as shown in FIG. 6, unlike the treating equipment 1 ofEmbodiment 1, a treating equipment 102 of this embodiment comprises areducing material-feeding portion 15 provided for the third heating oven13. The reducing material-feeding portion 15 is connected with the thirdheating oven 13 through a reducing material passageway 35 having a valve305 mounted thereon. Embodiment 4 is similar to Embodiment 1 in otherpoints.

In treating the steel dust 7 by using the treating equipment 1, thesteel dust 7 is fed from the feeding portion 10 to the first heatingoven 11 in which the steel dust 7 is heated at about 400° C. for onehour to recover chlorine and water therefrom.

Then, the steel dust 7 is fed to the second heating oven 12 in which avacuum having a vacuum degree of 0.5 Torr is produced so that the steeldust 7 is heated therein at about 600° C. for one hour to recoverfluoride and lead.

Then, a vacuum is produced at a vacuum degree of 0.5 Torr in the thirdheating oven 13 to which the reducing material 8 has been fed from thereducing material-feeding portion 15, and the steel dust 7 which haspassed the lead recovery process is fed to the third heating oven 13 sothat the steel dust 7 and the reducing material 8 are mixed together toobtain the to-be-treated mixed material 70.

Then, in the third heating oven 13 in which the vacuum state ismaintained, the to-be-treated mixed material 70 is heated for two hoursat 900° C. higher than the temperature set in the lead recovery process.As a result, zinc is reduced and vaporized to recover metallic zinc bythe metal recovery container 53.

After the zinc recovery process is completed, the residue 79 iscompression-molded into a briquette 795 by the compressor 141 of thebriquette machine 14 in which the vacuum state is maintained. In thismanner, a series of the treatments is completed. Similarly to Embodiment1, the respective valves are opened and closed to move the material ineach process switching time. In the treating times, the valves areclosed.

Embodiment 4 is similar to Embodiment 1 in other points.

Tables 7 through 9 show the results obtained by sampling and analyzingthe components of the steel dust 7 obtained after the respectiveprocesses finish, the components of the to-be-treated mixed material 70,and the components of the material obtained from the metal recoverycontainer 53.

Table 7 shows the values of the representative components of the steeldust 7 obtained immediately after the lead recovery process finishes. Asindicated in table 7, the lead (Pb) and the fluorine (F) contained inthe steel dust 7 at the initial stage shown in table 1 have beenrecovered sufficiently.

Table 8 shows the values of the representative components of theto-be-treated mixed material 70 obtained immediately after the zincrecovery process finishes, namely, the representative components of theresidue 79. As indicated in table 8, the zinc (Zn) contained in thesteel dust 7 at the initial stage shown in table 1 has been recoveredsufficiently.

Table 9 shows the values of the components of the material obtained fromthe metal recovery container 53 in the zinc recovery process. Asindicated in table 9, the recovered material contains the metallic zincat a high purity of 92.0%. The purity is greater than that in Embodiment1, which indicates that because the reducing reaction of the zinc can berestrained in the lead recovery process, the recovery of the zinc can beaccomplished mainly in the zinc recovery process and thus the recoverypercentage of the zinc can be improved in Embodiment 4.

The operation of this embodiment is similar to that of Embodiment 1 inother points.

                  TABLE 7                                                         ______________________________________                                        Value of components contained in to-be-treated mixed material after lead      recovery process (Embodiment 4)                                               Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             35.7   20.5   4.49 0.24 6.50 0.62 0.50 0.05 Bal-                        at %                                              ance                        ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Value of components contained in residue (Embodiment 4)                       Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             70.2   0.01   5.40 0.30 6.70 0.65 0.53 0.05 Bal-                        at %                                              ance                        ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Value of recovered metallic zinc (Embodiment 4)                               Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             0.66   92.0   0.01 0.02 0.01 0.01 0.20 0.10 6.99                        at %                                                                          ______________________________________                                    

Embodiment 5

In this embodiment, as shown in FIG. 7, the chlorine recovery processand the lead recovery process which are performed in Embodiment 1 aredone in the atmospheric environment as a chlorine and lead recoveryprocess 910 by heating the to-be-treated mixed material one time.

The steel dust 7 and the reducing material 8 of this embodiment aresimilar to those of Embodiment 1. The treating equipment which is usedin this embodiment does not have the second heating oven 12, unlike thetreating equipment 1 of Embodiment 1.

Embodiment 5 is similar to Embodiment 1 in other points.

In treating the steel dust 7 in this embodiment, initially, the steeldust 7 and the reducing material 8 are mixed together to obtain theto-be-treated mixed material 70.

Then, the to-be-treated mixed material 70 is fed to the first heatingoven in which the to-be-treated mixed material 70 is heated at about600° C. in the atmospheric environment for two hours to perform thechlorine and lead recovery process 910 of recovering lead, chlorine,fluoride, and water.

Then, with the completion of the chlorine and lead recovery process 910,the to-be-treated mixed material 70 is fed to the third heating oven inwhich a vacuum having a vacuum degree of 0.5 Torr is produced. Then, thezinc recovery process of recovering metallic zinc by heating theto-be-treated mixed material 70 for two hours at 900° C. higher than thetemperature set in the chlorine and lead recovery process 910 is carriedout.

Then, the residue is compression-molded into a briquette in the residuerecovery process, similarly to Embodiment 1. In this manner, a series ofthe treatments is completed.

Tables 10 through 12 show the results obtained by sampling and analyzingthe components of the to-be-treated mixed material 70 after therespective processes finish and the components of the material obtainedfrom the metal recovery container 53.

Table 10 shows the values of the representative components of theto-be-treated mixed material 70 obtained immediately after the chlorineand lead recovery process is completed. As indicated in table 10, thechlorine (C1), the lead (Pb), and the fluorine (F) contained in thesteel dust 7 at the initial stage shown in table 1 have been recoveredsufficiently.

In this embodiment, the chlorine and lead recovery process is carriedout in the atmospheric environment without producing a vacuum. The lead,the chlorine, the fluorine, and the water are volatilized by placing theto-be-treated mixed material 70 in a reducing atmosphere at a hightemperature. Thus, the lead, the fluorine, and the like can be reliablyrecovered by placing the to-be-treated mixed material 70 therein for thevolatilization time thereof.

Table 11 shows the values of representative components of theto-be-treated mixed material 70 immediately after the zinc recoveryprocess finishes, namely, the representative components of the residue79. As indicated in table 11, the zinc (Zn) contained in the steel dust7 at the initial stage shown in table 1 has been recovered sufficiently.

Table 12 shows the values of the components of the material obtainedfrom the metal recovery container 53 in the zinc recovery process. Asindicated in table 12, the obtained material contains the metallic zincat a high purity of 92.0%. The purity is higher than that in Embodiment1, which indicates that because the reducing reaction of the zinc can berestrained by performing the chlorine and lead recovery process in theatmospheric environment, the recovery of the zinc can be accomplishedmainly in the zinc recovery process and thus, the recovery percentage ofthe zinc can be improved in Embodiment 5.

The operation of this embodiment is similar to that of Embodiment 1 inother points.

                  TABLE 10                                                        ______________________________________                                        Value of components contained in to-be-treated mixed material after lead      recovery process (Embodiment 5)                                               Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             35.7   20.5   4.49 0.24 6.50 0.62 0.40 0.01 Bal-                        at %                                              ance                        ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        Value of components contained in residue (Embodiment 5)                       Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             70.2   0.01   5.40 0.30 6.70 0.65 0.41 0.01 Bal-                        at %                                              ance                        ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                        Value of recovered metallic zinc (Embodiment 5)                               Com-                                                                          ponent                                                                              Fe     Zn     Mn   Pb   Ca   Al   Cl   F    O                           ______________________________________                                        Content                                                                             0.66   92.0   0.01 0.02 0.01 0.01 0.01 0.01 Bal-                        at %                                              ance                        ______________________________________                                    

In Embodiments 1 through 5, one heating oven is specifically used foreach process, but one heating oven may be used for a plurality ofprocesses by adopting a method of sequentially changing the heatingcondition.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides a method of treatinga zinc oxide-containing waste capable of recovering metallic zinctherefrom at a high purity and accomplishing the on-site treatment ofthe waste.

What is claimed is:
 1. A treating method of recovering zinc in the metalstate from a waste containing the zinc in the oxide state, lead,chlorine, fluorine, and water, comprising:a mixing process of mixing thewaste and a reducing material together to obtain a to-be-treated mixedmaterial; a chlorine recovery process of recovering the chlorine and thewater by heating the to-be-treated mixed material; a lead recoveryprocess of recovering the fluorine and the lead by heating theto-be-treated mixed material under a vacuum state; a zinc recoveryprocess of reducing and vaporizing the zinc to recover metallic zinc byheating the to-be-treated mixed material at a temperature higher thanthat set in the lead recovery process, with the vacuum state maintained;and a residue recovery process of recovering a residue of theto-be-treated mixed material.
 2. The treating method according to claim1, wherein the to-be-treated mixed material is heated at 40-600° C. inthe chlorine recovery process.
 3. The treating method according to claim1, wherein the to-be-treated mixed material is heated at 200-600° C. inthe lead recovery process.
 4. The treating method according to claim 3,wherein the reducing material consists of car dust comprising organicsubstances recovered from materials of discarded automotive bodies. 5.The treating method according to claim 1, wherein the to-be-treatedmixed material is heated at 600-1,100° C. in the zinc recovery process.6. The treating method according to claim 1, wherein in the residuerecovery process, the residue is recovered by compression-molding theresidue into a briquette, with the vacuum state maintained.
 7. Thetreating method according to claim 1, wherein the reducing materialconsists of one or more industrial wastes selected from iron-containingindustrial wastes containing Fe and/or FeO and carbon-containingindustrial wastes containing carbon.
 8. The treating method according toclaim 1, wherein the reducing material consists of car dust comprisingorganic substances recovered from materials of discarded automotivebodies.
 9. The treating method according to claim 1, wherein the degreeof vacuum in the vacuum state in each of the processes is 0.001-20 Torr.10. A treating method of recovering zinc in the metal state from a wastecontaining the zinc in the oxide state, lead, chlorine, fluorine, andwater, comprising:a chlorine recovery process of recovering the chlorineand the water by heating the waste; a lead recovery process ofrecovering the fluorine and the lead by heating the waste in a vacuumstate; a mixing process of mixing a reducing material with the wastewith the vacuum state maintained to obtain a to-be-treated mixedmaterial; a zinc recovery process of reducing and vaporizing the zinc toobtain metallic zinc by heating the to-be-treated mixed material, withthe vacuum state maintained; and a residue recovery process ofrecovering a residue of the to-be-treated mixed material.
 11. Thetreating method according to claim 10, wherein the waste is heated at40-900° C. in the chlorine recovery process.
 12. The treating methodaccording to claim 10, wherein the waste is heated at 200-900° C. in thelead recovery process.
 13. The treating method according to claim 10,wherein the to-be-treated mixed material is heated at 600-1,100° C. inthe zinc recovery process.
 14. The treating method according to claim10, wherein in the residue recovery process, the residue is recovered bycompression-molding the residue into a briquette, with the vacuum statemaintained.
 15. The treating method according to claim 10, wherein thereducing material consists of one or more industrial wastes selectedfrom iron-containing industrial wastes containing Fe and/or FeO andcarbon-containing industrial wastes containing carbon.
 16. The treatingmethod according to claim 10, wherein the reducing material consists ofcar dust comprising organic substances recovered from materials ofdiscarded automotive bodies.
 17. The treating method according to claim10, wherein the degree of vacuum in the vacuum state in each of theprocesses is 0.001-20 Torr.
 18. A treating method of recovering zinc inthe metal state from a waste containing the zinc in the oxide state,lead, chlorine, fluorine, and water, comprising:a mixing process ofmixing the waste and a reducing material together to obtain ato-be-treated mixed material; a chlorine and lead recovery process ofrecovering the lead, the chlorine, the fluorine, and the water byheating the to-be-treated mixed material; a zinc recovery process ofreducing and vaporizing the zinc to obtain metallic zinc by heating theto-be-treated mixed material in a vacuum state; and a residue recoveryprocess of recovering a residue of the to-be-treated mixed material. 19.The treating method according to claim 18, wherein the to-be-treatedmixed material is heated at 40-750° C. in the chlorine and lead recoveryprocess.
 20. The treating method according to claim 18, wherein theto-be-treated mixed material is heated at 600-1,100° C. in the zincrecovery process.
 21. The treating method according to claim 18, whereinin the residue recovery process, the residue is recovered bycompression-molding the residue into a briquette, with the vacuum statemaintained.
 22. The treating method according to claim 18, wherein thereducing material consists of one or more industrial wastes selectedfrom iron-containing industrial wastes containing Fe and/or FeO andcarbon-containing industrial wastes containing carbon.
 23. The treatingmethod according to claim 18, wherein the degree of vacuum in the vacuumstate in each of the processes is 0.001-20 Torr.